Mass spectrometry is a powerful tool in disparate areas of chemistry, but its characteristic strength of sensitivity can be an Achilles heel when studying highly reactive organometallic compounds. A quantity of material suitable for mass spectrometric analysis often represents a tiny grain or a very dilute solution, and both are highly susceptible to decomposition due to ambient oxygen or moisture. This complexity can be frustrating to chemists and analysts alike: the former being unable to get spec-

Ring-closing metathesis (RCM) is an elegant means of forming cyclic structural elements in both simple and complex molecules. Mechanistically, the reaction cycle is well understood, though subtle details concerning the...

Ring-closing metathesis (RCM) is an elegant means of forming cyclic structural elements in both simple and complex molecules. Mechanistically, the reaction cycle is well understood, though subtle details concerning the fate of the catalyst and the appearance of yield-reducing by-products remain to be fully deciphered. We applied real-time analysis using electrospray ionization mass spectrometry (ESI-MS) to probe the RCM reaction, including studying the dynamics of all charged species in the reaction mixture and investigating the nature of the by-products formed. The catalyst of choice was Grubbs’ second-generation catalyst. The principal findings included the fact that for slower reactions, by-products appeared that differed in mass from the starting material and product by increments of CH2; that isomerization reactions were responsible for these by-products; and that the catalyst decomposes to form charged products including [ClPCy3]+, [HPCy3]+, and the imidazolinium salt of the N-heterocyclic carbene (NHC) ligand. In cases where RCM is slow, isomerization reactions play a disproportionate part in affecting yield of the desired product.

Kinetic analysis of catalytic reactions is a powerful tool for mechanistic elucidation but is often challenging to perform. Establishing order in a catalyst is achieved by running several reactions at different loadings, which is complicated by the challenge of maintaining consistent run-to-run experimental conditions. We present Continuous Addition Kinetic Elucidation (CAKE), which involves steadily injecting catalyst into the reaction, and following reaction progress over time to generate a plot whose shape is dependent only on the order in reactant and in catalyst. Modelling the curve (using a convenient web tool) allows the catalyst and reactant order to be determined, as well as the rate constant and the amount of any catalyst poison present.

Kinetic analysis of catalytic reactions is a powerful tool for mechanistic elucidation but is often challenging to perform. Establishing order in a catalyst is achieved by running several reactions at different loadings, which is complicated by the challenge of maintaining consistent run-to-run experimental conditions. We present Continuous Addition Kinetic Elucidation (CAKE), which involves steadily injecting catalyst into the reaction, and following reaction progress over time to generate a plot whose shape is dependent only on the order in reactant and in catalyst. Modelling the curve (using a convenient web tool) allows the catalyst and reactant order to be determined, as well as the rate constant and the amount of any catalyst poison present.